[dard]

I actually work on NEO Surveyor telescope (surveying for dangerous asteroids), writing the simulation code use to track expected performance. So simulating +20 million asteroids and what will be visible during the mission. Motion is how we determine if there is an asteroid or just some static sky source (IE: star).

However your comment is not correct, everything moves, even in the days leading up to a potential impact things are constantly in motion. The only asteroids which appear stationary actually tend to be quite far away and just happen to be moving at just the right speed.

Things which are close to us, even impactors tend to have large angular velocities, very VERY few things come directly radially in. A part of this is that the Earth is rotating, if you are familiar with the parallax effect then the Earths rotation causes parallactic motion of the asteroids when close. IE, take a photo, wait 4 hours, and you, an observer on Earth, has now moved. The geometry has to be just right for close objects to be stationary, and a different observing position on Earth (or space) will see the object moving even if you see it stationary.

[phkahler]

Earth is about 8000mi across. The moon is about 239000mi away. Looking at it from opposite sides would be about 0.016 degrees of angular displacement. And that's a couple days from impact.

>> So simulating +20 million asteroids and what will be visible during the mission.

How many impacts do you simulate? These are the ones we care most about, and I still think they will be the hardest to detect.

[dard]

Here is a simulation I did in response to your comment, this is ~6 million impactors and their on sky velocity as they approach Earth. Dotted black line is our expected detectability limit, anything to the right of that is detectable. On sky velocity is measured in degrees / day.

https://www.dardahlen.com/6m_impactor_vel.png

[phkahler]

Thanks, that's really cool. And the detectability line is under 0.01 degrees per day, so the parallax from opposite sides of the earth is well within detectable at lunar distance. You also confirm that the detectability (due to motion) is dropping as the time to impact decreases, but this is apparently not a problem. Leave it to projects run by physicists to have exquisite measurement precision ;-)

[reaperman]

Amazing work to share so rapidly in this context! The results of your simulation and this discussion will stick with me for a long time. Thank you!

[dorkNiner]

thanks I think that that's really kind of scary, but motivational as to putting up a moon colony so that we just have a 2n base. H But I have. have a few questions. If you've got a minute, must be nerve wracking to work there.

looks like it would be coming from the sun's direction because it is kind of a. dominating force , but i wonder why a couple days after a flyby is when they are often detected. Is it just because the sun is able to light/heat it up more?

Also, I'm wondering what software you use to to do the modeling for one. And if it's open source. and if it's reversible , so you can back it up and fix positions when new datas comes in

https://en.wikipedia.org/wiki/Fermi%E2%80%93Pasta%E2%80%93Ul... That was done at Los Alamos with a Maniac and the first version was fixed point, but as you can see it looks chaotic, but then there's a semi ring. There's a repetition. So I I'm guessing that's why that we care about are flybys. They go by once and at some point they'll come back.

https://www.josstam.com/reversible

  This might help if you click the reversible to use  fixed point. you can go back and and retrace.. the steps even with a rough integration. 

as soon as you have a correction for any of them, you can place that correction. By reversing the entire model or the solver.

I'm guessing there's such a cloud of objects you use something like. Fluid solver, even if you had to do that to some other body, then may have had an influence on the body that's under investigation, and you have new data for that, it might help to make the prediction more accurate. And without introducing any discontinuities in the model, if the past positions help determine the future ones going back.

You can see here (Stam) that even though it's chaotic like an N body problem, there is a semi ring and it repeats. So what appears to be maybe chaotic over time would be periodicity of the lineup. Then it seems, though, when certain planets are lined up. It's more likely that it's gonna have this this. confluence of Of gravitational influence. that will bring it in our direction. I'm thinking thinking Jupiter, Mars, the moon and the sun and the earth in between. Jupiter all the way to the earth is basically one orbit. At that velocity S50 kilometers uh second.

Also, I wonder if. the if something hit the back of the moon, would we even notice that until we go to the back of the moon or with a lunar reconnaissance or over and we find some craters that have direct impacts so that it would have could have been our planet killer. I'm sure there's quite a few up there with some some markings that will indicate that it probably injected some heavy metal right at that very crater. A direct hit. The moon was in the way because the the lineup of the two bodies ,that caused the dynamic in the first place. I'm guessing here.

Thanks again for making that chart.